Some things stay constant in life and those things are often "luxuries". Computers, TVs, furniture, cars and such stay close in price and if they go up there is always a newer model (which is what happens with carrs) as an option that is still in the cheap price range.
I think there is a threshold people are willing to pay for certain things.
Also I bet a high % of people that buy porn memberships are not the same people that buy new furniture, cars or other big ticket items very often (since that income range is the highest % of people alive anyway). Certain things in life need to stay the same to be viable and survive.
Now if EVERY site upped the membership to $50 then great.
